The overarching aim of this program is to develop small molecule tools for understanding ion channel protein function associated with the highly complex ionic mechanisms of electrical transmission in neuronal cells. Naturally occurring guanidinium poisons - tetrodotoxin, saxitoxin, gonyautoxin 2/3, and zetekitoxin AB - form the bedrock of these investigations. Despite evident differences in molecular size and topology, all four molecules are exquisitely potent blockers of voltage-gated sodium ion channels (NaV) that operate by occluding the extracellular mouth of the ion conductance pore (Site I). Studies of NaV structure, of which there exist ten mammalian isoforms, and function have been advanced with the availability from natural sources of tetrodotoxin, saxitoxin, and small number of structurally related forms. In the absence of crystallographic data, molecules such as gonyautoxin 2/3, zetekitoxin AB, and designed saxitoxin mimics in combination with protein mutagenesis experiments would enable current homology models of the channel pore to be challenged and refined. Knowledge accrued from these types of studies could lead to new chemical agents patterned after the guanidinium toxins that demonstrate NaV subtype specific activity. Such tools are desirable for mapping the spatial and temporal distribution of specific channel isoforms in developing or injured neurons. As NaV channels are considered lead actors in mechanisms for inflammation and neuropathic pain response, drugs that act on specific channel subtypes could represent next-generation therapies for the treatment of such ailments. PUBLIC HEALTH RELEVANCE: We are interested in understanding at a molecular level how nerve cells conduct electricity and how the process of electrical signaling is affected when a nerve is injured. Chemical synthesis is the engine that drives our program and will make possible the preparation of selective reagents that can be used to investigate these complex biological phenomena. Results from these studies could help guide the development of new therapies for the treatment of acute and/or chronic pain. [unreadable] [unreadable] [unreadable]